/Engine/Source/Runtime/SignalProcessing/Public/DSP/VoiceProcessing.h
Buffers InAudio and renders any non-silent audio to OutAudio. Returns the number of samples written to OutAudio. The number of samples returned will only be less than NumSamples if the signal becomes audible mid-buffer. We do not return partial buffers when returning from an audible state to a silent state. This should also work in place, i.e. if InAudio == OutAudio.
int32 ProcessBuffer ( const float * InAudio, float * OutAudio, int32 NumSamples )